Stick corrosion inhibitors



having from 6 to 18 carbon atoms.

United States Patent Cfitice 2,805,202 Patented Sept. 3, 1957 STICKCORROSION INHIBITORS Charles C. Nathan, Bellaire, Tex., assignor to TheTexas Company, New York, N. Y., a corporation. of Delaware No Drawing.Application September 30, 1955, Serial No. 537,905

10 Claims. (Cl. 252-855).

The present invention relates to inhibiting corrosion in oil welltubing, and is particularly concerned with an improved stick type ofinhibitor which can be dropped into oil well tubing.

In my copending application Serial No. 371,167, filed July 29, 1953, ofwhich the present application is a continuation-in-part, there isdisclosed a method for inhibiting metal bodies against corrosion bymaintaining in contact with such a body at least one symmetricalthiourea compound corresponding to the formula H s H RI Q'-i JI I-Rwherein R is an aliphatic radical having from to 8 carbon atoms such asan unsubstituted radical or a mono aryl substituted radical, for examplen-hexyl, B-phenyl ethyl, or a-methyl benzyl.

Compounds of the type mentioned above which have been employedsuccessfully in my novel method are:

1. s-Di-n hexyl thiourea (melting point 40 C):

i i Gem-om-n-o-n-om-omQ 3. s-Di-ot-methyl benzyl thiourea (melting point163 C.):

OH: H H CH3 Efforts were made to compound a satisfactory stick inhibitorby mixing such a thiourea with paraflin waxes of the type conventionallyemployed as binders in such sticks. It was found, however, that suchmixtures are unsatisfactory because they have no mechanical strength andwill not hold together. One possible explanation of this failure is thatparafiin wax is a non-polar material while the thiourea is a polarmaterial.

After considerable experimentation I have found, surprisingly, that asatisfactorily coherent stick inhibitor can be made up by mixing thethiourea compound with amorphous synthetic wax. One such wax comprisesat least one high molecular weight n-primary aliphatic amide Anothercomprises at least one high molecular weight polyethylene glycol fattyacid ester wherein the fatty acid group has from 12 to 18 carbon atoms,said ester having a high molecular weight between 4000 and 6000. Iascribe my success with such a mixture to the fact that the syntheticwaxes are amorphous materials having polar groups such as hydroxyl,ether, and amide groups which are characterized by their ability tosolubilize the thiourea compound thus being compatible therewith.

In preparing the novel stick inhibitor compositions of this invention,the synthetic wax-and-thiourea mixture is heated to a temperature abovethe melting point of the mixture, after which they are thoroughly mixedtogether, and with any other ingredients needed. The mixture is thenallowedto cool as rapidly as possible and the synthetic wax to solidify.Rapid cooling eflects the formation of fine crystals and prevents thesettling of the weighting material, e. g., barytes or other high densitymaterials such as iron oxide.

Any of several different n-primary aliphatic amide synthetic waxes maybe used for the present invention, several of which are described in thefollowing table,

percentages being by weight:

The above amides usually contain a small amount of unreacted fatty acid,such as 5% which does not adversely affect the stick inhibitor.

A synthetic wax composed of a polyethylene glycol stearate has also beenused successfully which is a hard, tough, tan wax having a molecularweight of about 6000, a melting point of 140 to 143 C., a flash point of285 C., and a specific gravity of 0.97 at 20 C. compared to water at thesame temperature.

In preparing stick inhibitors in accordance with the invention theproportion of the synthetic wax binder required is relatively small,usually ranging from 1 to 15% by weight based on the thiourea and anyother ingredients.

While from the corrosion prevention standpoint all that is required is atwo component mixture of the proper thiourea with synthetic wax, it issometimes necessary to incorporate in the stick other ingredients suchas weighting materials which will impart a high enough specific gravityso that the stick will sink in well fluid. A commonly used weightingmaterial is barytes.

Example I A stick inhibitor was made up by heating to 110 C. 18 grams ofamide type synthetic wax A mixed with 360 grams of thiourea No. 2, and360 grams of barytes. Upon solidification of the melted synthetic waxand thiourea the resulting solid stick was found to be strongly bondedtogether. It was then successfully introduced into an oil well.

Example II A stick inhibitor was made up by heating to 110 C. a mixtureof 7.5 grams of amide type synthetic wax A, 7.5 grams of amide typesynthetic wax B, 300 grams of thiourea No. 2, and 300 grams of barytes.The synthetic wax and thiourea melted and were then allowed to solidify.A strongly bonded stick was obtained. It was then successfullyintroduced into an oil well.

Example III A stick inhibitor was made up by heating to 110 C. a mixtureof 10 grams of the synthetic wax composed of a polyethylene glycolmonostearate having a molecular weight of 6000, as described above, andgrams of thiourea No. 2. The mixture was then cooled and solidified toform a strongly bonded stick having a specific gravity of 1.05.

Example IV A stick inhibitor was made up by heating to C,

a mixture of grams "or the synthetic wax composed of I a polyethyleneglycol monostearate having a molecular Weight of 6000, of the typedescribed above, 100 grams of thiourea No. 2, and 110 grams of barytes.Upon cooling the mixture the synthetic wax and thiourea solidified and astrongly bonded stick inhibitor resulted having a specific gravity of1.4,a softening point of 80 (0., and a melting point of 90 C. 1

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim: 8 V

1. A bonded solid corrosion inhibiting composition of mattercharacterized 'by high mechanical strength consisting essentially of atleastonej thiourea compound having from 6 to 18 carbon atoms in thealiphatic acid radical.

2. A composition of matter in accordance with claim 1 wherein saidthiourea is s-di-n hexyl thiourea. 3. A composition of matter inaccordance with claim 1 wherein said thiourea is s-di-p-phenyl ethylthiourea. 4. A composition of matter in accordance with claim 1 whereinsaid thiourea is s-di-a-methyl benzyl thiourea. 5. A composition ofmatter in accordance with claim 1 wherein said synthetic wax consistsessentially of at least one highmolecular weight polyethylene glycolfatty acid ester wherein thefatty acid group has from 12 to 18 carbonatoms, said ester having a molecular weight between 4000. and 6000. r

6. In a method for inhibiting against corrosion a steel tube in a, wellwherein petroleum fluid associated with a corrosive water solution isflowing, by introducing into said solution at least one thioureacompound corresponding to the formula wherein R is an aliphatic radicalhaving from 5 to 8 carbon atoms, the improvement comprising droppingthrough said tube a bonded solid body consisting essentially of saidthiourea compound bonded with an N-primary aliphatic amide having from 6to 18 carbon atoms in the aliphatic acid radical.

7. A solid corrosion inhibiting composition consisting essentially of atleast one thiourea corresponding to the in which R is an aliphaticradical having from 5 to 8 3 carbon atoms and 'mixedtherewith as abinder anI N- primary aliphatic amide having from 6 to 18 carbon atomsin the aliphatic acid radical.

8. A composition according to claim 7 in which said binder consists ofhexadecanoic acid amide. V 9. A composition according to claim 7 inwhich said binder consists of octadecanoicacid amide.

10. A composition according to claim 7 in which said binder consitsfofoctadecenoic acid amide.

References Cited in the file of this patent UNITED STATES PATENTS2,599,385 Gross et all June 3, 1952 2,602,779 Moyer et al. July 8, 19522,728,727 Marsh Dec. 27, 1955 2,698,295

Cardwell et a1 Dec. 28, 1954 "at of. .MA

1. A BONDED SOLID CORROSION INHIBITING COMPOSITION OF MATERCHARACTERIZED BY HIGH MECHANICAL STRENGTH CONSISTING ESSENTIALLY OF ATLEAST ONE THIOUREA COMPOUND CORRESPONDING TO THE FORMULA